Translumenal angioplasty is a technique of dilating blocked blood vessels from the inside, thus avoiding the need for more extensive surgical intervention. In balloon angioplasty a deflated balloon catheter is placed across the narrowed segment of the artery and then the balloon is inflated so as to transmit circumferential pressure and compress the plaque. This procedure more or less normalizes the internal lumenal size, following which natural healing generally occurs over a period of weeks or months. Even where a laser technique is used to evaporate a plaque blockage and create a channel, supplemental balloon dilatation is often advisable, in order to achieve an adequate internal lumenal size. In many cases it may be desirable, in order to expand the narrowed lumen and to maintain the opening, to inflate the balloon catheter while inside a stent (tube or coil), which provides a mechanical scaffolding and prevents the possible complete blockage of the artery that may occur due to unexpected tear with balloon angioplasty. The use of stent angioplasty, when considered appropriate, improves the chances of success, both immediately and on a long-term basis.
In recent years, the realization that the use of stents may be medically advantageous has led to a great increase in patent activity, in this field. A variety of stents, both metal and polymeric (or a combination of both) as well as stents in cylindrical and helical configurations (see e.g., U.S. Pat. No. 6,027,516 (Kolobow et al.)), have been proposed.
Methods for the manufacture of polymeric stents, as e.g., by extruding or molding operations, are by now well-known (see e.g. U.S. Pat. No. 5,085,629 (Goldberg), U.S. Pat. No. 5,510,077 (Dinh et al.), U.S. Pat. No. 5,527,337 (Stack et al.) and U.S. Pat. No. 5,972,027 (Johnson). Consequently, current research efforts appear to be directed to particular structures or compositions imparting desired properties to such stents, rather than to methods of manufacture per se.
One approach to the subject of polymeric stents has been to make an expandable stent with a memory. Thus, U.S. Pat. Nos. 5,163,952 and 5,607,467 (Froix) describe a cylindrical stent with a predetermined diameter and a memory of greater diameter, whereby on application of certain stimuli (heat, liquid absorption or pH change) the stent attempts to assume the greater diameter. Examples of polymers said to exhibit such properties are mainly copolymers of various methacrylates.
WO 9942147A1 (Langer et al.) also discloses shape memory polymer compositions, which are at least in part biodegradable. The compositions may comprise block copolymers containing both hard and soft segments, of which at least one segment is thermoplastic, or may utilize crosslinked sift segments in absence of hard segments. In one example, the hard segment was a hydroxy-terminated oligoglycolate, and the soft segment was a hydroxy-terminated oligolactate/glycolate or a poly(caprolactone)diol, linked by reaction with an alkanediisocyanate; in another example, thermoset poly(caprolactone)dimethacrylates were prepared. This document mentions stents as one of numerous proposed applications of the disclosed compositions, but gives no details as to how this might be affected in practice.
Polymeric stents with a memory appear to have significant drawbacks. In particular, expansion of such a manufactured stent in situ would seem to be dependent on the built-in memory intrinsic to a particular polymer composition. There is an obvious danger that the consequent defined expansion may be too little or too much, and it would be evident that this kind of haphazard approach to the treatment of heart conditions would be entirely inappropriate.
According to the present invention, however, such a disadvantage is avoided by providing a stent which can be expanded as necessary in the individual circumstances of a particular patient.
While in a preferred utility of the invention, a stent will be attached to a balloon catheter; the technique of attachment is generally well-known and forms no part of the present invention per se. Merely by way of example, a method for securing a stent to a balloon catheter is described in U.S. Pat. No. 5,860,966 (Tower).
Also, as will be evident from a description of the invention which follows, stents may be adapted for the purposes of drug delivery, nevertheless, use of stents as drug delivery systems is also well-known and does not per se form part of the present invention. Illustrative examples of stents used as drug delivery systems are afforded by U.S. Pat. No. 5,383,928 (Scott et al.), U.S. Pat. No. 5,464,450 (Busceni et al.), U.S. Pat. No. 5,498,238 (Shapland et al.), U.S. Pat. No. 5,554,182 (Dinh et al.), U.S. Pat. No. 5,591,227 (Dinh et al.), U.S. Pat. No. 5,811,447 (Kunz et al.), U.S. Pat. No. 5,843,172 (Yan et al.), U.S. Pat. No. 5,954,706 (Sahatjian), U.S. Pat. No. 5,972,027 (Johnson), 5,980,551 (Summers et al.) and U.S. Pat. No. 6,013,099 (Dinh et al.).
U.S. Pat. No. 4,826,945 (Cohn et al.) describes biodegradable surgical articles made from α-hydroxycarboxylic acid/polyoxyalkylene block copolymers.
Catheters and stents having various geometrical configurations are known, e.g. they may be of hollow cylindrical configuration and additionally be corrugated, or have a circumferentially corrugated or pleated section, see for example U.S. Pat. No. 4,403,985 (Boretos), U.S. Pat. No. 4,784,639 (Patel) and U.S. Pat. No. 5,725,547 (Chuter).
Many polymeric stents/surgical articles require heat curing in situ. The stents/surgical articles of the present invention avoid the necessity for this inconvenient requirement.
The entire contents of the above-mentioned U.S. patents and WO published patent application are incorporated herein by reference.